1. Field of the Invention
The present invention relates to a method of authenticating playback information reproduced from a disk-type recording medium, a disk playback apparatus for playing back a disk-type recording medium, and an entertainment apparatus which uses information reproduced from a disk-type recording medium.
2. Description of the Related Art
In recent years, disk-type recording mediums which store information recorded as pits according to a predetermined format are finding use as major information storage mediums. One of the features of the disk-type recording mediums is that they have a large information storage capacity.
Some of the disk-type recording mediums, which are in widespread use, incorporate an information protection measure to protect the stored information against unauthorized duplication. Those disk-type recording mediums are protected to prevent the stored information from being copied without the consent of the author.
Protected disk-type recording mediums are played back by a dedicated disk playback apparatus.
Before the disk playback apparatus plays back a protected disk-type recording medium, the disk playback apparatus decides whether a predetermined code for protecting stored information, i.e., a security code, has been written in the protected disk-type recording medium or not. Stated otherwise, the disk playback apparatus plays back a protected disk-type recording medium after confirming that the protected disk-type recording medium is a legitimate disk. Such a disk playback system is generally known as a security system.
There have been illegal attempts to reproduce information from non-protected disk-type recording mediums with a special device attached to a disk playback apparatus.
Heretofore, it has been customary to read a security code written in a certain area on a protected disk-type recording medium loaded in the disk playback apparatus thereby to authenticate that protected disk-type recording medium is a legitimate disk. The above special device operates as if it could read a security code though it is in fact incapable of reading the data of the security code, so that it can authenticate a disk-type recording medium which should not be authenticated in reality.
Using the above special device, an illegally copied disk-type recording medium which should not be authenticated can be authenticated in an authenticating process when it is to be played back, and can be played back by a disk playback apparatus to which the special device is connected.